JP2021015780A - Lithium ion secondary battery and manufacturing method thereof - Google Patents

Abstract

To provide a lithium ion secondary battery in which high capacity and low internal resistance are compatible.SOLUTION: A lithium ion secondary battery 1 has a single cell 11 with a first electrode 2, a separator 3 laminated on the first electrode 2, and a second electrode 4 laminated on the separator 3. The first electrode 2 has a porous material 21 containing one kind or more of LLZ-based solid electrolyte, out of lantern zirconate lithium and lantern zirconate lithium doped with an atom other than Li atom, La atom and Zr atom, and having a pore 211, and an active material 22 held in the pore 211. The separator 3 contains one kind or more of LLZ-based solid electrolyte of lantern zirconate lithium doped with an atom other than Li atom, La atom and Zr atom, and one kind or more of B atom, P atom and Si atom.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

In recent years, as a battery for automobiles and electronic devices, a so-called all-solid-state battery in which a solid electrolyte is interposed between a positive electrode and a negative electrode has been proposed. For example, Patent Document 1 includes a dense central layer containing a dense electrolyte material and having a first surface and a second surface opposite to the first surface, and the first of the dense central layers. Described is a battery comprising a first electrode arranged on the surface of the dense center layer and a second electrode arranged on the second surface of the dense central layer. Further, in Patent Document 1, the electrolyte material of the central layer, the first porous electrolyte material contained in the first electrode, and the second porous electrolyte material contained in the second electrode are the same. The points that may be used are described.

Special Table 2019-507377

When the central layer and the porous electrolyte material are laminated as in the battery of Patent Document 1, for example, the green sheet of the central layer containing the electrolyte particles and the binder and the porous material containing the electrolyte particles, the binder and the pore-forming material are included. By sintering the laminate with the green sheet of the quality electrolyte material, it is possible to integrally form the central layer and the porous electrolyte material.

However, as in Patent Document 1, when the central layer and the porous electrolyte material are composed of the same electrolyte, the electrolyte particles also crystal grow in the central layer and the porous electrolyte material during sintering. .. Therefore, when the heating temperature at the time of sintering is increased, the pore volume of the porous electrolyte material becomes small due to the crystal growth of the electrolyte particles, which tends to cause a decrease in the capacity of the battery. On the other hand, if the heating temperature at the time of sintering is lowered, there is a problem that the bonding between the electrolyte particles in the central layer and the porous electrolyte material becomes insufficient, which tends to increase the internal resistance of the battery.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a lithium ion secondary battery capable of achieving both high capacity and low internal resistance and a method for manufacturing the same.

One aspect of the present invention is the first electrode (2) and
The separator (3) laminated on the first electrode and
It has a single cell (11) provided with a second electrode (4, 402) laminated on the separator.
The first electrode is
It contains one or more of LLZ-based solid electrolytes doped with lithium lanthanum zirconate and an atom other than Li (lithium) atom, La (lantern) atom, and Zr (zylconyl) atom. A porous body (21) having pores (211) and
With the active material (22) retained in the pores,
The separator is
Has a relative density of 80% or more,
Lithium lanthanum zircate and one or more LLZ-based solid electrolytes doped with atoms other than Li, La, and Zr atoms, and B (boron) atom and P (phosphorus) atom. And a lithium ion secondary battery (1, 102) containing one or more of Si (silicon) atoms.

Another aspect of the present invention is the method for manufacturing a lithium ion secondary battery according to the above aspect.
A first layer containing the LLZ-based solid electrolyte and a pore-forming material, a first layer containing the LLZ-based solid electrolyte, and a sintering aid containing one or more of B, P, and Si atoms. A laminating process of superimposing two layers to form a laminated body,
A method for manufacturing a lithium ion secondary battery, which comprises a co-sintering step of integrally forming the porous body and the separator by sintering the laminated body at a temperature of 700 ° C. or higher and lower than 1050 ° C. It is in.

The porous body in the lithium ion secondary battery is one or more LLZ-based one or more of LLZ doped with lithium lanthant zirconate (that is, LLZ) and atoms other than Li atom, La atom and Zr atom. A solid electrolyte is contained, and the separator contains an LLZ-based solid electrolyte and one or more of B atoms, P atoms and Si atoms. The B atom, P atom and Si atom are atoms contained in the sintering aid used in the manufacturing process of the lithium ion secondary battery.

By using the above-mentioned atom-containing sintering aid in the manufacturing process of the lithium ion secondary battery, while suppressing the excessive progress of crystal growth of the LLZ-based solid electrolyte in the porous body during sintering, The LLZ-based solid electrolyte in the separator can be sufficiently crystal-grown. As a result, both high capacitance and low internal resistance can be achieved at the same time.

Further, in the method for manufacturing a lithium ion secondary battery, a laminated body is produced by superimposing a first layer which becomes a porous body after sintering and a second layer which becomes a separator after sintering. By sintering this laminated body, the porous body and the separator can be integrally formed. Since the second layer contains a sintering aid containing one or more of B, P, and Si atoms, crystals of the LLZ-based solid electrolyte in the porous body during sintering. The LLZ-based solid electrolyte in the separator can be sufficiently crystal-grown while suppressing the excessive progress of growth. As a result, both high capacitance and low internal resistance can be achieved at the same time.

As described above, according to the above aspect, it is possible to provide a lithium ion secondary battery capable of achieving both high capacity and low internal resistance, and a method for manufacturing the same.
The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

FIG. 1 is a cross-sectional view showing a main part of the lithium ion secondary battery according to the first embodiment. FIG. 2 is a cross-sectional view showing a main part of a lithium ion secondary battery having a porous body on both the first electrode and the second electrode in the second embodiment. FIG. 3 is an SEM image of the porous body of the test body T12 in the experimental example. FIG. 4 is an SEM image of the separator of the test body T12 in the experimental example. FIG. 5 is an SEM image of the porous body of the test body T14 in the experimental example. FIG. 6 is an SEM image of the separator of the test body T14 in the experimental example.

(Embodiment 1)
An embodiment relating to the lithium ion secondary battery and a method for manufacturing the same will be described with reference to FIG. The lithium ion secondary battery 1 has a single cell 11 including a first electrode 2, a separator 3 laminated on the first electrode 2, and a second electrode 4 laminated on the separator 3. There is. The first electrode 2 contains one or more LLZ-based solid electrolytes out of lithium lanthanidylconate (LLZ) and lithium lanthanandylconate doped with atoms other than Li atom, La atom, and Zr atom, and many of them. It has a porous body 21 having pores 211 of the above, and an active material 22 held in the pores 211. The separator 3 contains one or more LLZ-based solid electrolytes of lithium lanthanozirconate doped with atoms other than LLZ and Li atoms, La atoms, and Zr atoms, and B atom, P atom, and Si atom. One or more of them are included. The relative density of the separator 3 is 80% or more.

The lithium ion secondary battery 1 may have one single cell 11 or may have a plurality of single cells 11. For example, the lithium ion secondary battery 1 of this embodiment has one single cell 11. A current collector 12 is laminated on the surface of the first electrode 2 and the surface of the second electrode 4 in the single cell 11, respectively. The lithium ion secondary battery 1 can be charged or discharged by adding or connecting a power generation device to these current collectors 12. As the current collector 12, for example, a composite material in which a conductive powder such as carbon or a conductive oxide is dispersed in a conductor such as a metal foil or a metal plate or an insulator such as glass can be used. ..

Although not shown in the figure, when the lithium ion secondary battery 1 has a plurality of single cells 11, the current collectors 12 and the single cells 11 are alternately overlapped with each other via the current collector 12. A plurality of single cells 11 can be electrically connected. For example, by superimposing the current collector 12 and the single cell 11 so that one surface of the current collector 12 is in contact with the first electrode 2 and the other surface is in contact with the second electrode 4. A plurality of single cells 11 can be connected in series. Further, by superimposing the current collector 12 and the single cell 11 so that the current collector 12 is interposed between the electrodes 2 and 4 of the same type, a plurality of single cells 11 can be connected in parallel. ..

The first electrode 2 may be a positive electrode or a negative electrode. Specifically, the first electrode 2 of this embodiment is a positive electrode.

Further, the shape of the first electrode 2 can take various forms. For example, although not shown in the figure, the first electrode 2 of the present embodiment has a rectangular plate shape formed by the porous body 21.

The porous body 21 contains LLZ and one or more LLZ-based solid electrolytes of lithium lanthanozirconate doped with atoms other than Li atom, La atom, and Zr atom. That is, the porous body 21 may be composed of an LLZ-based solid electrolyte, or may contain a LLZ-based solid electrolyte and a substance other than the LLZ-based solid electrolyte.

For example, the porous body 21 may further contain one or more of B atom, P atom and Si atom. That is, in the manufacturing process of the lithium ion secondary battery 1, a sintering aid containing these atoms may be added to the porous body 21. In this case, the heating temperature at which the porous body 21 is sintered can be lowered, and the energy consumption in the manufacturing process of the lithium ion secondary battery 1 can be further reduced.

When a sintering aid is also added to the porous body 21 in the manufacturing process of the lithium ion secondary battery 1, the total content of B atoms, P atoms and Si atoms in the porous body 21 is calculated in the separator 3. It is preferably less than the total content of B, P and Si atoms. In this case, it is possible to promote the crystal growth of the LLZ-based solid electrolyte in the separator 3 and more reliably suppress the excessive crystal growth of the LLZ-based solid electrolyte in the porous body 21. As a result, the increase in the relative density of the porous body 21 can be suppressed more effectively, and the capacity of the lithium ion secondary battery 1 can be further increased.

The porous body 21 has pores 211. The active material 22 is retained in the pores 211 of the porous body 21. In addition to the active material 22, a conductive auxiliary agent, another solid electrolyte different from the LLZ-based solid electrolyte, a liquid electrolyte, or the like may be held in the pores 211.

The pores 211 of the porous body 21 may have a continuous pore structure, for example, as shown in FIG. The relative density of the porous body 21, that is, the ratio of the apparent density of the entire porous body 21 including the pores 211 to the density of the portion of the porous body 21 excluding the pores 211 is, for example, 60% or less. can do. Further, from the viewpoint of maintaining the shape of the porous body 21, the relative density of the porous body 21 can be set to, for example, 30% or more.

The relative density of the porous body 21 is a value calculated based on a three-dimensional reconstructed image obtained by a FIB / SEM (that is, a focused ion beam / scanning electron microscope) tomography method. More specifically, processing of the sample by the FIB device and observation of the processed surface by SEM are repeated to acquire a plurality of SEM images. By reconstructing these SEM images on image analysis software, a three-dimensional reconstructed image of the sample is obtained. Then, the obtained three-dimensional reconstructed image is subjected to a binarization treatment so that the boundary between the porous body 21 and the rest is not impaired. The relative density of the porous body 21 is the ratio of the total volume of the LLZ-based solid electrolyte and the volume of the sintering aid to the apparent volume of the porous body 21 calculated based on the binarized image obtained as described above. And.

The active material 22 can be appropriately selected according to the polarity of the first electrode 2. For example, when the first electrode 2 is a positive electrode, a sulfur-based active material containing a sulfur atom or an oxide-based active material made of an oxide can be used as the active material 22 of the first electrode 2. Examples of the sulfur-based active material, specifically, simple and lithium sulfide sulfur (Li ₂ S), can be lithium using doped sulfur and the like. Specific examples of the oxide-based active material include lithium cobalt oxide (LiCoO ₂ ), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , lithium manganate (LiMnO ₂ ), and lithium iron phosphate (LiFePO). ₄ ) etc. can be used.

When the first electrode 2 is a positive electrode, it is preferable that the active material 22 contains a sulfur atom. In this case, the capacity of the lithium ion secondary battery 1 can be further increased. Specifically, the active material 22 of this embodiment is a simple substance of sulfur.

When the first electrode 2 is a negative electrode, metallic lithium, carbon, Li ₄ Ti ₅ O _12, or the like can be used as the active material 22 of the first electrode 2.

As shown in FIG. 1, the separator 3 is integrally formed with the porous body 21 of the first electrode 2. The relative density of the separator 3 is 80% or more. As a result, the separator 3 can suppress a short circuit between the first electrode 2 and the second electrode 4. From the viewpoint of more reliably suppressing a short circuit between the first electrode 2 and the second electrode 4, the relative density of the separator 3 is preferably 90% or more, and more preferably 95% or more.

The separator 3 contains one or more LLZ-based solid electrolytes of LLZ doped with atoms other than LLZ and Li atoms, La atoms, and Zr atoms, and one of B atoms, P atoms, and Si atoms. Or two or more types are included. That is, in the manufacturing process of the lithium ion secondary battery 1, a sintering aid containing these atoms may be added to the separator 3. The sintering aid containing these atoms melts before the LLZ-based solid electrolyte when the porous body 21 and the separator 3 are sintered in the manufacturing process of the lithium ion secondary battery 1. Then, the crystal growth of the LLZ-based solid electrolyte can be promoted by the contact between the melt of the sintering aid and the LLZ-based solid electrolyte.

Therefore, by adding a sintering aid to the separator 3 in the manufacturing process of the lithium ion secondary battery 1, the rate of crystal growth of the LLZ-based solid electrolyte in the separator 3 during sintering can be increased. As a result, it is possible to promote the crystal growth of the LLZ-based solid electrolyte in the separator 3 while suppressing the excessive progress of the crystal growth of the LLZ-based solid electrolyte in the porous body 21.

From the viewpoint of enhancing the effect of promoting crystal growth of the LLZ-based solid electrolyte, it is preferable to use a sintering aid having a low melting point. Further, the melting point of the sintering aid tends to be the lowest for the sintering aid containing B atoms, and tends to be higher in the order of the sintering aid containing P atoms and the sintering aid containing Si atoms. Therefore, from the viewpoint of promoting the crystal growth of the LLZ-based solid electrolyte in the separator 3, it is most preferable that the separator 3 contains a B atom, and it is next preferable that the separator 3 contains a P atom.

Further, when the sintering aid is added to the porous body 21 in the manufacturing process of the lithium ion secondary battery 1, the melting point of the sintering aid used for the porous body 21 is the sintering aid used for the separator 3. It is preferably higher than the melting point of the agent. That is, when the separator 3 contains B atoms, it is preferable that the porous body 21 contains one or two of P atoms and Si atoms. When the separator 3 contains P atoms, the porous body 21 preferably contains Si atoms.

In this way, by making the melting point of the sintering aid in the porous body 21 higher than the melting point of the sintering aid in the separator 3, the crystal growth of the separator 3 is promoted and the porous body 21 is excessive. Crystal growth can be suppressed more reliably. As a result, the increase in the relative density of the porous body 21 can be suppressed more effectively, and the capacity of the lithium ion secondary battery 1 can be further increased.

The content of B atom, P atom and Si atom in the separator 3 is preferably 12 mol% or more and 65 mol% or less with respect to the La (lanthanum) atom in the separator 3. In this case, the amount of the LLZ-based solid electrolyte in the separator 3 can be sufficiently secured to enhance the lithium ion conductivity, and the effect of promoting sintering by the sintering aid can be obtained.

The LLZ-based solid electrolyte contained in the separator 3 may be the same as or different from the LLZ-based solid electrolyte of the porous body 21. The average crystal grain size of the LLZ-based solid electrolyte in the separator 3 is preferably larger than the average crystal grain size of the LLZ-based solid electrolyte in the porous body 21. In this case, the relative density of the separator 3 can be made higher, and the relative density of the porous body 21 can be made lower. As a result, the lithium ion conductivity can be further improved and the internal resistance can be further reduced. Further, the amount of lithium that can be stored in the pores 211 can be increased to increase the capacity of the lithium ion secondary battery 1.

The average crystal grain size of the LLZ-based solid electrolyte in the porous body 21 and the separator 3 can be measured by the following method. That is, first, the lithium ion secondary battery 1 is cut in the stacking direction of the porous body 21 and the separator 3 to expose the cross section. This cross section is observed with a scanning electron microscope to obtain an SEM image. Then, the maximum diameters of the crystals of the plurality of LLZ-based solid electrolytes existing in the SEM image are measured. The average value of these maximum diameters is taken as the average crystal grain size of the LLZ-based solid electrolyte. The number of crystals of the LLZ-based solid electrolyte used for calculating the average crystal grain size is not particularly limited, but the more the number of crystals used for calculating the average crystal grain size is, the more accurate the value is calculated. Can be done. From this point of view, the number of crystals of the LLZ-based solid electrolyte used for calculating the average crystal particle size is preferably 10 or more, and more preferably 20 or more.

The second electrode 4 is laminated on the surface of the separator 3 opposite to the surface on which the first electrode 2 is provided. The second electrode 4 has a polarity different from that of the first electrode 2. That is, when the first electrode 2 is configured as a positive electrode, the second electrode 4 is configured as a negative electrode. When the first electrode 2 is configured as a negative electrode, the second electrode 4 is configured as a positive electrode.

The configuration of the second electrode 4 is not particularly limited. For example, the second electrode 4 may be composed of only an active material different from the active material 22 of the first electrode 2, or the active material may be contained in the pores of the porous body as in the first electrode 2. It may be a retained configuration.

The active material of the second electrode 4 can be appropriately selected according to the polarity of the second electrode 4. For example, the second electrode 4 of this embodiment is a lithium plate made of metallic lithium as an active material.

Next, a method for manufacturing the lithium ion secondary battery 1 of the present embodiment will be described. The method for manufacturing the lithium ion secondary battery 1 of the present embodiment is a laminating step of superimposing a first layer which becomes a porous body 21 after sintering and a second layer which becomes a separator 3 after sintering to prepare a laminated body. It also has a co-sintering step of integrally forming the porous body 21 and the separator 3 by sintering the laminated body at a temperature of 700 ° C. or higher and 1050 ° C. or lower.

In the laminating step, the specific method for producing the first layer and the second layer can take various aspects. For example, in one aspect of the laminating step, a separator mixture containing an LLZ-based solid electrolyte, a solvent, a sintering aid, and a binder is prepared, and then the separator mixture is molded into a sheet. A green sheet as the first layer can be produced. As the LLZ-based solid electrolyte used in the separator mixture, for example, a powder of solid electrolyte crystals can be used.

The cumulative 50% particle diameter (that is, d50) of the LLZ-based solid electrolyte used in the separator mixture on a volume basis is preferably 1.0 μm or less. In this case, since the surface area of the LLZ-based solid electrolyte in the first layer becomes larger, the crystal growth of the LLZ-based solid electrolyte during sintering can be further promoted. As a result, the relative density of the separator 3 can be made higher. Further, in this case, the thickness of the first layer can be easily reduced while suppressing the formation of defects such as pinholes in the first layer. As a result, the thickness of the obtained separator 3 can be made thinner.

As the sintering aid, an inorganic compound containing one or two of B atom, P atom and Si atom can be used. From the viewpoint of increasing the capacity of the lithium ion secondary battery 1, the sintering aids include Li ₃ BO ₃ , Li ₆ B ₄ O ₉ , Li ₄ B ₂ O ₅ , Li BO ₂ , B ₂ O ₃ , and so on. It is preferable to use one or more of Li ₃ PO ₄ , Li ₄ SiO _4, and Li ₂ SiO ₃ .

Further, after preparing a mixture for electrodes containing an LLZ-based solid electrolyte, a solvent, a pore-forming material, and a binder, the mixture for electrodes is formed into a sheet to prepare a green sheet as a second layer. can do. As the pore-forming material, for example, acrylic resin powder or the like can be used. The electrode mixture may contain the above-mentioned sintering aid in addition to the LLZ-based solid electrolyte, solvent, pore-forming material and binder.

A laminated body can be obtained by superimposing the green sheet of the porous body 21 and the green sheet of the separator 3 thus obtained and then integrating them by a method such as thermocompression bonding.

Further, in another aspect of the laminating step, a green compact as the first layer is produced by compression molding a mixed powder containing the LLZ-based solid electrolyte and the pore-forming material. A mixed powder containing an LLZ-based solid electrolyte and a sintering aid is placed on this green compact and compression molded to form a green compact as a second layer on the first layer. Can be obtained.

In the co-sintering step, the laminated body obtained in the laminating step is heated at a temperature of 700 ° C. or higher and lower than 1050 ° C. When the heating temperature in the co-sintering step is within the above-mentioned specific range, the sintering aid melts before the LLZ-based solid electrolyte, and a melt of the sintering aid is generated. By contacting the melt of the sintering aid with the LLZ-based solid electrolyte, the crystal growth of the LLZ-based solid electrolyte can be promoted. Therefore, the crystal growth of the LLZ-based solid electrolyte in the separator 3 can be promoted by heating at the temperature in the specific range.

On the other hand, the precursor of the porous body 21 contains a pore-forming material. Therefore, in the co-sintering step, the pore-forming material first disappears and the pores 211 are formed. After that, the LLZ-based solid electrolyte in the precursor of the porous body 21 starts crystal growth. At this time, the precursor of the porous body 21 does not contain a sintering aid, or is configured so that the effect of the sintering aid is lower than that of the precursor of the separator 3. Therefore, the rate of crystal growth of the LLZ-based solid electrolyte in the porous body 21 is slower than that of the LLZ-based solid electrolyte in the separator 3.

Therefore, in the co-sintering step, by heating the laminate at a temperature in the specific range, the LLZ in the separator 3 is suppressed while suppressing the excessive progress of crystal growth of the LLZ-based solid electrolyte in the porous body 21. The system solid electrolyte can be sufficiently crystal-grown.

The heating temperature in the co-sintering step is preferably 900 ° C. or higher. In this case, the crystal growth rate of the LLZ-based solid electrolyte can be increased in both the porous body 21 and the separator 3 while maintaining the above-mentioned magnitude relationship of the crystal growth rate.

On the other hand, if the heating temperature in the co-sintering step becomes excessively high, crystal growth is likely to occur in the state of the LLZ-based solid electrolyte alone. Therefore, the crystal growth of the LLZ-based solid electrolyte in the porous body 21 may proceed excessively, leading to a decrease in the capacity of the lithium ion secondary battery 1. By setting the heating temperature in the co-sintering step to less than 1050 ° C., such a problem can be avoided. From the same viewpoint, the heating temperature in the co-sintering step is preferably 1000 ° C. or lower.

As described above, the porous body 21 and the separator 3 can be integrally formed. Then, the active material 22 is held in the pores 211 of the porous body 21 thus obtained, and the second electrode 4 is arranged on the back surface of the separator 3 on the side having the porous body 21. The lithium ion secondary battery 1 can be formed.

The method of retaining the active material 22 in the pores 211 of the porous body 21 can take various aspects. For example, the active material 22 may be retained in the pores 211 by filling the pores 211 with the active material 22 itself. Further, for example, after filling the pores 211 with the precursor of the active material 22, the precursor can be converted into the active material 22 by performing a treatment such as heating.

(Embodiment 2)
In this embodiment, another aspect of the second electrode is shown. In addition, among the symbols used in the present and subsequent forms, the same codes as those used in the existing forms represent the same components and the like as those in the existing forms unless otherwise specified. In the lithium ion secondary battery 102 of this embodiment, the porous body 21 is referred to as a first porous body 21, and the active material 22 of the first electrode 2 is referred to as a first active material 22. The first electrode 2 of the present embodiment has the same configuration as that of the first embodiment except that the first active material 22 is lithium doped with lithium. Further, the separator 3 of the present embodiment has the same configuration as that of the first embodiment.

As shown in FIG. 2, the second electrode 402 of the present embodiment includes a second porous body 41 containing an LLZ-based solid electrolyte and having pores 411, a second active material 42 held in the pores 411, and the second active material 42. have.

The specific configuration of the second porous body 41 in the second electrode 402 is the same as that of the first porous body 21 in the first electrode 2. That is, the second porous body 41 may be composed of an LLZ-based solid electrolyte, or may contain a LLZ-based solid electrolyte and a substance other than the LLZ-based solid electrolyte. Further, the LLZ-based solid electrolyte contained in the second porous body 41 may be the same as or different from the LLZ-based solid electrolyte contained in the first porous body 21 and the separator 3.

Further, the second porous body 41 may further contain one or more of B atom, P atom and Si atom. That is, in the manufacturing process of the lithium ion secondary battery 1, a sintering aid containing these atoms may be added to the second porous body 41. In this case, the heating temperature when sintering the second porous body 41 can be lowered, and the energy consumption in the manufacturing process of the lithium ion secondary battery 102 can be further reduced.

When a sintering aid is also added to the second porous body 41 in the manufacturing process of the lithium ion secondary battery 1, the total content of B atoms, P atoms and Si atoms in the second porous body 41 is calculated. It is preferably less than the total content of B, P and Si atoms in the separator 3. In this case, it is possible to promote the crystal growth of the LLZ-based solid electrolyte in the separator 3 and more reliably suppress the excessive crystal growth of the LLZ-based solid electrolyte in the second porous body 41. As a result, the increase in the relative density of the second porous body 41 can be suppressed more effectively, and the capacity of the lithium ion secondary battery 1 can be further increased.

From the same viewpoint, the melting point of the sintering aid used for the second porous body 41 is preferably higher than the melting point of the sintering aid used for the separator 3. More specifically, when the separator 3 contains B atoms, it is preferable that the second porous body 41 contains one or two of P atoms and Si atoms. When the separator 3 contains P atoms, it is preferable that the second porous body 41 contains Si atoms.

The second porous body 41 has pores 411. The second active material 42 is retained in the pores 411 of the second porous body 41. In addition to the second active material 42, a conductive auxiliary agent, another solid electrolyte different from the LLZ-based solid electrolyte, a liquid electrolyte, or the like may be held in the pores 411.

The pores 411 of the second porous body 41 may have a continuous pore structure. The relative density of the second porous body 41 can be, for example, 60% or less. Further, from the viewpoint of maintaining the shape of the second porous body 41, the relative density of the second porous body 41 can be, for example, 30% or more. The relative density of the second porous body 41 is the same as the relative density of the first porous body 21, and is a three-dimensional reconstruction obtained by the FIB / SEM (that is, focused ion beam / scanning electron microscope) tomography method. It is a value calculated based on the image.

Similar to the first active material 22, the second active material 42 can be appropriately selected according to the polarity of the second electrode 402. Specifically, the second active material 42 of this embodiment is metallic lithium.

Further, the lithium ion secondary battery 102 of the present embodiment is obtained by laminating the precursor of the first porous body 21, the precursor of the separator 3, and the precursor of the second porous body 41 in the laminating step. , Can be produced by the same production method as in the first embodiment. The method for producing the precursor of the second porous body 41 is the same as that of the precursor of the first porous body 21.

The lithium ion secondary battery 102 of the present embodiment can exhibit the same effects as those of the first embodiment.

(Experimental example)
In this example, the heating temperature in the co-sintering step and the sintering aid are variously changed to prepare a test body in which the separator 3 and the porous body 21 are laminated, and the relative density of the porous body 21 and the separator 3 is adjusted. It was measured. The method for producing the test body will be described below. The method for measuring the relative density is as described above.

・ Specimen T1
In preparing the test body T1, first, a mixture for an electrode containing LLZ powder, Li ₃ BO ₃ as a sintering aid, acrylic resin as a pore-forming material, a solvent, and a binder was prepared. .. The content of the sintering aid in the electrode mixture was adjusted so that the molar ratio of B atom to La (lanthanum) atom of LLZ was 0.13. This electrode mixture was molded into a sheet using an applicator to prepare a green sheet as the first layer. The thickness of the first layer was set to 300 μm. The melting point of Li ₃ BO ₃ is 820 ° C.

Separately from this, a mixture for a separator containing LLZ powder, Li ₃ BO ₃ as a sintering aid, a solvent, and a binder was prepared. The content of the sintering aid in the separator mixture was adjusted so that the molar ratio of B atom to La atom of LLZ was 0.37. This separator mixture was molded into a sheet using an applicator to prepare a green sheet as the second layer. The thickness of the second layer was set to 300 μm.

The first layer and the second layer thus formed were cut to a desired size, and both were superposed to obtain a laminated body. A warm isotropic press is performed on this laminate to bring the two green sheets into close contact with each other, and then the laminate 3 and the porous body 21 are integrally formed by heating at the temperatures shown in Table 1 in the air atmosphere. did. From the above, a test body T1 was obtained. Table 1 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in the test body T1.

-Test specimens T2-T4
The method for producing the test specimens T2 to T4 is the same as that of the test specimen T1 except that the type and the amount of the sintering aid added are changed as shown in Table 1. Table 1 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in these test bodies. The melting point of Li ₃ PO ₄ , which is the sintering aid used in the test piece T2, is 840 ° C. The melting point of Li ₂ SiO ₃ , which is a sintering aid used in the test piece T3, is 1200 ° C.

・ Specimen T5
The method for producing the test piece T5 is the same as that of the test piece T1 except that the amount of the sintering aid added to the electrode mixture is the same as the amount of the sintering aid added to the separator mixture. Table 1 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in the test body T5.

・ Specimen T6
The method for producing the test body T6 is the same as that of the test body T1 except that the sintering aid is not added to the electrode mixture and the separator mixture. Table 1 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in the test body T6.

-Test specimens T7 to T10
The method for producing the test bodies T7 to T10 is the same as that of the test body T1 except that the type and the amount of the sintering aid added are changed as shown in Table 2. Table 2 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in these test bodies.

・ Specimen T11
The method for producing the test body T11 is the same as that of the test body T1 except that the sintering aid is not added to the electrode mixture. Table 2 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in the test body T11.

-Test body T12 and test body T13
The method for producing the test body T12 and the test body T13 is the same as that of the test body T11 except that the heating temperature at the time of sintering is set to the temperature shown in Table 2. Table 2 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in these test bodies.

・ Specimen T14
The method for producing the test body T14 is the same as that of the test body T1 except that the amount of the sintering aid added and the heating temperature at the time of sintering are changed as shown in Table 3. Table 3 shows the relative densities of the porous body 21 and the relative densities of the separator 3 in the test body T14.

For the test body T12 and the test body T14, the average crystal grain size of LLZ contained in the porous body 21 and the separator 3 and the electric conductivity of the test body were measured by the following methods.

-Average crystal grain size-
The test piece was cut in the stacking direction of the porous body 21 and the separator 3 to expose the cross section. This cross section was observed with a scanning electron microscope, and an SEM image at a magnification of 5000 was obtained. The SEM image of the porous body 21 in the test body T12 is shown in FIG. 3, and the SEM image of the separator 3 is shown in FIG. The SEM image of the porous body 21 in the test body T14 is shown in FIG. 5, and the SEM image of the separator 3 is shown in FIG. As shown in FIGS. 3 to 6, the LLZ crystals in the porous body 21 and the separator 3 are granular, and the adjacent LLZ crystals are integrated by being connected to each other.

Among the LLZ crystals present in these SEM images, the maximum diameter was measured for 20 or more randomly selected crystals. Then, the average value of these maximum diameters was taken as the average crystal grain size of LLZ. Table 3 shows the average crystal grain size of LLZ in each of the porous body 21 of the test body T12, the separator 3 of the test body T12, the porous body 21 of the test body T14, and the separator 3 of the test body T14.

-Electrical conductivity of the test piece-
After applying gold paste to both end faces in the thickness direction of the test piece, baking was performed at 600 ° C. to form terminals. An impedance measuring device (“1260A” manufactured by Solartron) and a test piece were connected via these terminals, and the electric resistance value was measured in the frequency range of 10 μHz to 32 MHz. The electric conductivity was calculated using the electric resistance value obtained as described above, the area of the end face in the thickness direction of the test piece, and the thickness of the test piece. Table 3 shows the electric conductivity of the test body T12 and the test body T14.

As shown in Table 1, in the manufacturing process of the test pieces T1 to T4, a sintering aid is used for both the porous body 21 and the separator 3. Further, the amount of the sintering aid added to the porous body 21 is smaller than the amount of the sintering aid added to the separator 3. Therefore, in these test bodies, it was possible to promote the crystal growth of LLZ in the separator 3 while suppressing the crystal growth of LLZ in the porous body 21.

On the other hand, in the test body T5, the type and amount of the sintering aid contained in the porous body 21 and the type and amount of the sintering aid contained in the separator 3 were the same, so that the porous body 21 contained the same. The LLZ and the LLZ in the separator 3 were similarly crystal-grown. As a result, in the test body T5, the pores 211 of the porous body 21 disappeared, leading to an increase in the relative density.

In the test body T6, no sintering aid was used in either the porous body 21 or the separator 3, so that the crystal growth of LLZ was insufficient. Therefore, the relative density of the separator 3 is low.

As shown in Table 2, the melting point of the sintering aid used for the porous body 21 in the test bodies T7 to T10 is higher than the melting point of the sintering aid used for the separator 3. Therefore, in these test bodies, it was possible to promote the crystal growth of LLZ in the separator 3 while suppressing the crystal growth of LLZ in the porous body 21.

Since the test body T11 and the test body T12 used the sintering aid only for the separator 3, it was possible to promote the crystal growth of the LLZ in the separator 3 while suppressing the crystal growth of the LLZ in the porous body 21. It was.

In the test body T13, the heating temperature at the time of sintering was excessively high, so that the LLZ in the porous body 21 and the LLZ in the separator 3 were similarly crystal-grown. As a result, in the test body T5, the pores 211 of the porous body 21 disappeared, leading to an increase in the relative density.

Since the test body T14 shown in Table 3 was heated at a temperature lower than the melting point of the sintering aid, 830 ° C., a melt of the sintering aid could not be sufficiently formed. Therefore, the test body T14 could not sufficiently crystal grow the LLZ in the separator 3, resulting in a decrease in lithium ion conductivity.

The present invention is not limited to the above embodiments and experimental examples, and can be applied to various embodiments without departing from the gist thereof.

1,102 Lithium-ion secondary battery 2 1st electrode 21 Porous medium 211 Pore 22 Active material 3 Separator 4,402 2nd electrode

Claims (7)

With the first electrode (2)
The separator (3) laminated on the first electrode and
It has a single cell (11) provided with a second electrode (4, 402) laminated on the separator.
The first electrode is
A porous body containing one or more LLZ-based solid electrolytes of lithium lanthanus zirconate and lithium lanthanum zirconate doped with atoms other than Li atom, La atom, and Zr atom, and having pores (211). (21) and
With the active material (22) retained in the pores,
The separator is
Has a relative density of 80% or more,
Lithium lanthanum zircate and one or more LLZ-based solid electrolytes doped with atoms other than Li, La, and Zr atoms, and one of B, P, and Si atoms. Lithium ion secondary batteries (1, 102) containing seeds or two or more. The porous body contains one or more of B atom, P atom and Si atom, and the total content of B atom, P atom and Si atom in the porous body is a separator. The lithium ion secondary battery according to claim 1, which is less than the total content of B atoms, P atoms and Si atoms in the above. The lithium ion secondary battery according to claim 2, wherein the separator contains a B atom, and the porous body contains one or two of P atoms and Si atoms. The lithium ion secondary battery according to claim 2, wherein the separator contains a P atom and the porous body contains a Si atom. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the average crystal grain size of the LLZ-based solid electrolyte in the separator is larger than the average crystal grain size of the LLZ-based solid electrolyte in the porous body. .. The method for manufacturing a lithium ion secondary battery according to any one of claims 1 to 5.
A second layer containing the LLZ-based solid electrolyte and a pore-forming material, and a second layer containing the LLZ-based solid electrolyte and a sintering aid containing one or more of B, P, and Si atoms. A laminating process of laminating layers to form a laminated body,
A method for manufacturing a lithium ion secondary battery, which comprises a co-sintering step of integrally forming the porous body and the separator by sintering the laminated body at a temperature of 700 ° C. or higher and lower than 1050 ° C. .. The lithium ion according to claim 6, wherein the sintering aid is one or more of Li ₃ BO ₃ , B ₂ O ₃ , Li ₃ PO ₄ , Li ₄ SiO _4, and Li ₂ SiO _4. How to manufacture a secondary battery.